Superheater support in a steam generator



United States Patent 13,s30,s3s

3,368,536 2/l968 Sullivan Primary Examiner Kenneth W. Sprague AnomeysCarlton F. Bryant, Eldon H. Luther, Robert L. Olson, John F. Carney, Richard H. Berneike, Edward L. Kochey, Jr. and Lawrence P. Kessler through the horizontal support tubes in parallel with the low I temperature superheater and discharges into the inlet header for the high temperature superheater section.

[72] Inventor Johann G. Sailer Chateauguay Center, Province of Quebec, Canada [21] Appl. No. 823,715 [22] Filed May 12,1969 [45] Patented Sept. 29, 1970 [73] Assignee Combustion Engineering, Inc.

Windsor, Connecticut a corporation of Delaware [54] SUPERHEATER SUPPORT IN A STEAM GENERATOR 9 Claims, 4 Drawing Figs.

[52] US. Cl l22/5l0 [5 l] Int. Cl F22b 37/24 [50] Field of Search l22/6A, 494, 510

[56] References Cited UNITED STATES PATENTS 3.060.909 l0/l962 Ott 122/510 A d l E Z 7 27L j 10 Patented Sept. 29, 1970 Sheet FIG-1 ATTORNEY Patented Sept. 29, 1970 Sheet 'Ar rozNeY Patented Sept. 29,1970

Sheet Pie-3 INIVENTOR. J'OHANN 6.- $411.52

ATTORNEY Patented Sept. 29, 1970 Sheet INVENTOZ J'OHANN 6'. SAILER 6 x ayx A T rolzusY SUPERHEATER SUPPORT lN A STEAM GENERATOR BACKGROUND OF THE INVENTION This invention relates to steam generators and particularly to anapparatus for the support of horizontal heating surfaces In steam generators.

Large steam generators superheat the steam generated to a final temperature by passing the steam through tubes which are located in the flue gas stream. In many units vertical pendent sections are used. In order to achieve several advantages which accrue from a fully drainable superheater, some units have the entire superheater made of horizontal assemblies. These assemblies then are supported either on hanger tubes or supported on their own terminals with ties between the adjacent elements of the superheater.

.Since the steam temperature increases in passing through these horizontal superheaters, each element tends to expand a little more than the preceding one. In some locations the expansion is sufficiently small to permit welding and therefore entirerestraint of the movement. In other situations ties are used between the adjacent elements so that they may freely expand relative to one another. Where a substantial amount of superheater surface must be supported, excessive loads are put on these spacers thereby interfering with free movement. In the superheatersection where the steam temperature is high and high gas temperature is encountered, the spacers are susceptible to high temperature corrosion, particularly where they must be of substantial length and therefore are not cooled by the tubes to which they are attached.

Where vertical hanger tubes are used to carry the superheater elements, they are usually welded to each of the horizontal elements. Since these vertical tubes are welded to the expanding horizontal elements, they are forced out of the vertical position and must bend to accommodate the expanded lengths of the various superheater elements. This bending can create excessive stresses and eccentric loading in these hanger tubes. On the other hand, should the horizontal elements be slidingly supported from these hanger tubes, difficulty is encountered with the size of the slide support in the high temperature area since these supports cannot be adequately cooled by the tube. In order to avoid these problems the horizontal elements are sometimes cradled on a lug joining two vertical support tubes. This requires two tubes for each support arrangement.

' SUMMARY In my invention a low temperature horizontal superheater and a high temperature horizontal superheater are each supported on hanger tubes which are in turn supported from an upper elevation. The low temperature superheater is directly supported on these hanger tubes by welding the superheater elements to the vertical hanger tubes. The high temperature superheater section is indirectly supported from these vertical hanger tubes. A horizontal support tube passes transversely to the elements of the high temperature superheater and is welded to the vertical hanger tubes. The horizontal elements rest on the horizontal support tube either independently or in groups. Steam from the steam drum passes through this horizontal support tube in parallel with the low temperature superheater section so that heat absorbed by this horizontal support tube is contributed to the overall steam generator superheater.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation of a steam generator;

FIG. 2 is a rear elevation showing the surface arrangement in the rear gas pass;

FIG. 3 is a detail view showing the arrangement of the support tubes in the high temperature superheater; and I FIG. 4 is a detail of the high temperature superheater showinggroups ofthe horizontal elements for support purposes.

DESCRIPTION OF THE PREFERRED EMBODIMENT The steam generator illustrated in FIG. 1 has a furnace in which fuel is burned with the combustion gases passing outwardly through opening 12 to the top section ofa vertical flue 13. The gases pass downwardly through flue 13 and out through opening 14 to an air heater and stack (not shown).

Feedwater is supplied to the generator through feedwater line 15 to economizer inlet header [7. It passes through economizer heating surface 18 to the economizer outlet header 19 with the heated water passing upwardly through pipe 20 to steam drum 22.

Water from steam drum 22 at approximately saturation temperature passes through downcomer 23 to lower side wall header 24 and lower front wall header 25. Water from the lower header passes upwardly through tubes 27 which line the furnace walls with the rear wall of the furnace also being the front wall of the rear gas pass flue 13. This water at generally saturation temperature also passes upwardly through tubes 28 which line the rear wall offlue l3 and side wall tubes 29 which line the side walls of flue 13. The water together with the steam which is generated is connected to upper headers 32 and 33 and conveyed to the steam drum 22 where the water is separated and returned through downcomer 23.

The saturated steam from the steam drum 22 passes through steam lines 34 and 35 to low temperature superheater inlet header 37. It then passes through the low temperature superheater 38 and enters into low temperature superheater outlet header 39.

This slightly superheated steam passes from the low temperature superheater outlet header 39 through pipe 40 which contains a desuperheater, and conveys the steam to high temperature superheater inlet header 42. Steam from this header enters the high temperature superheater elements 43 where it is heated to a final steam temperature and passes to a final superheater outlet header 44 from which it is conveyed to a steam turbine (not shown).

Water at generally saturation temperature also passes from the lower headers 24 upwardly through hanger tubes 45. These tubes convey the fluid to upper support headers 47 from which the steam-water mixture formed in passing through the tubes is conveyed to the steam drum 22.

These hanger tubes 45 are supported at the upper elevation and pass between adjacent passes of tubes in the economizer 18 as well as the superheaters 38 and 43. The tubes on either side of the hanger tube are welded to the hanger tube in the economizer and superheater sections with this weld preferably being made by using a saddle to avoid undercutting the tubes during welding. By this arrangement all of the weight of these sections is carried directly on the hanger tubes. These vertical hanger tubes must flex slightly to absorb the differential expansion between the various elements welded to it. Since these welded elements are not operating at extremely high temperatures, the amount of expansion which may be absorbed is nominal as compared to the length over which these hanger tubes are able to flex. The tubes of the high temperature superheater section 43 are not directly welded to the hanger tubes. More than two hanger tubes may be used for each element if the length of the element requires more frequent support.

The wall tubes through which the superheater terminals pass and the vertical support tubes which carry the superheater are both at generally saturation temperature. Differential vertical movement between the superheater and the wall is minimized and stressing of the terminals passing through the walls is also minimized.

The support of the high temperature superheater section is more clearly shown in FIGS. 3 and 4 wherein the plurality of vertical hanger tubes 45 are welded to horizontal support tubes 48 using welding saddles 46. Steam is supplied to these support tubes 48 from the steam drum 22 through supply line 49. The steam is discharged from one of the support tubes to header 39 while the discharge from the other support tube is to header 42. While this steam bypasses the low temperature superheater section, it is in series flow relationship with the high temperature superheater section. Full steam flow passes through the critical high temperature superheater section, and

proper sizing of the support tube provides sufficient flow to protect it. Since the heat absorbed in this horizontal support tube goes towards superheating rather than evaporating, this support arrangement minimizes the depressing effect of heat absorbed by the support tubes on steam temperature thus combining the advantages of water cooled hanger tubes, which are kept at a minimum, with steam cooled supports.

The horizontal steam superheating elements of the high temperature section 43 are connected at the ends to form two intermeshed flow paths in each of the superheater assemblies. Some of these elements rest directly on the horizontal support tube 48. Other horizontal elements are supported in turn from these elements by the use of spacer supports. Ferritic spacer supports 50 are of the type which are solidly welded to the adjacent tubes. A group of these solid supports ties together four horizontal elements, so that a group of four tubes is supported from the horizontal support tube 48. The spacer between adjacent groups of four elements is omitted. Since as the steam proceeds upwardly, each element operates and at slightly higher temperature each element will expand slightly more. By limiting the group to approximately four elements, the temperature differential within the welded group is minimized. This group of four elements may then bow upwardly a slight amount to relieve the stresses which would be imposed. Some austenitic spacers may be used on the ferritic tubing in the very high gas temperature range, since the spacers operate at a temperature above that of the tubing.

The spacers 52 near the top of the assembly are of austenitic material and are also of the solidly welded type. A change in this structure takes place. however, where the superheating tubing changes from austenitic to ferritic material.

The lower portion of the superheater at location 53 is formed of ferritic material. Due to the higher temperature existing at the outlet section of the superheater, austenitic material must be used for sufficient strength. Since austenitic material expands at a greater rate than ferritic material, considerable horizontal expansion differential movement would occur between the horizontal ferritic and the adjacent austenitic elements even ifthey were at the same temperature. This expansion difference is magnified since the austenitic material operates at a higher temperature due not only to the high gas temperature at that location and the high steam temperature but due to the fact that the conductivity of austenitic material is lower than that of ferritic material, thereby resulting in a higher temperature. Because of this expansion differenee, spacers used where the material changes from ferritic to austenitic must be slip spacers. These slip spacers will carry the vertical load but will slide horizontally to allow for the expansion difference. While these slip spacers are successfully used they do occasionally bind, resulting in bowing of the tubes.

In the illustrated embodiment the use of all slip spacers is avoided. Space 51 is between the horizontal pass where the material changes from ferritic to austenitic. This pass is at one of the locations where the spacer is entirely omitted with the tubes above and below the space all being carried on their respective horizontal support tubes. All possibility of spacer binding is thereby eliminated.

With this support arrangement, only the horizontal support tube 48 is welded to the vertical hanger tubes. The superheater elements rest and slide on these horizontal support tubes. Therefore. longitudinal expansion of the superheater elements imposes no substantial force on the vertical hanger tubes and avoids the need for these tubes to flex in accordance with the expansion of the superheater. This is particularly important at the location where the material changes since the flexing of the hanger tubes would otherwise have to take place in a short vertical distance thereby resulting in a high bending stress in the hanger tubes. Also since the hanger tubes need not flex in accordance with the high temperature superheater, space requirements between the high temperature superheater and low temperature superheater is minimized. The only concern is minimal access for repair. Otherwise sufficient length would have to be left between the sections to permit flexing of the hanger tubes without overstressing.

While I have illustrated and described a preferred embodiment of my invention it is to be understood that such is merely illustrative and not restrictive and that variations and modifications may be made therein without departing from the spirit and scope of the invention. l therefore do not wish to be limited to the precise details set forth but desire to avail myself of such changes as fall within the purview of my invention.

l claim:

1. A fluid heater and a support arrangement for supporting the fluid heater within a steam generator; said steam generator having a vertical gas pass with hot gases flowing therethrough, and tubes lining the wall of vertical gas pass at generally uniform temperature, comprising: a first plurality of horizontal low temperature fluid heating elements located in said flue; a second plurality of horizontal high temperature fluid heating elements located in said flue at a location upstream with respect to gas flow of said first plurality of elements; a plurality of vertical hanger tubes passing through said flue, said hanger tubes being supported at an upper elevation and being welded to said first plurality of horizontal elements at a lower elevation, said hanger tubes being welded to support said first plurality of horizontal elements at two locations generally adjacent the ends thereof; horizontal support tubes welded to said hanger tubes and passing through the flue in a direction transverse to said second plurality of horizontal elements and immediately adjacent at least some of the elements, at least some of said second plurality of horizontal elements resting on said horizontal support tubes.

2. An apparatus as in claim 1 wherein said second plurality of horizontal high temperature fluid heating elements are connected at the ends to form a sinuous tubular flow path; said horizontal support tubes directly supporting only a portion of said second plurality of horizontal elements; support spacers between adjacent horizontal elements in the area adjacent the location of each horizontal support tube whereby the weight ofa plurality of the horizontal elements is indirectly carried on i said support tube.

3. An apparatus as in claim 2 wherein at one location between each pass of the horizontal support tubes the support spacers are omitted.

4. An apparatus as in claim 2 wherein a portion of the second plurality of horizontal fluid heating elements is of fer ritic material and located at the fluid inlet portion thereof while the remainder of second plurality of horizontal steam heating elements is of austenitic material and located near the outlet thereof.

5. The apparatus as in claim 4 wherein said support spacers are omitted between the horizontal passes where the horizon tal element material changes from ferritic to austenitic.

6. An apparatus as in claim 1 having a steam drum; and means for conveying steam from said steam drum directly to said horizontal support tube.

7. An apparatus as in claim 1 wherein said steam generator also has a steam drum; means for conveying steam from said steam drum through said first plurality of horizontal fluid heat ing elements; means for conveying steam from said first to said second plurality of horizontal fluid heating elements; said horizontal support tube being connected in parallel with said first plurality of horizontal elements but in series with said second horizontal elements whereby steam passing through the support tube bypasses said first plurality of steam heating elements.

8. An apparatus as in claim 5 wherein said steam generator also has a steam drum; means for conveying steam from said steam drum through said first plurality of horizontal fluid heating elements; means for conveying steam from said first to said second plurality of horizontal fluid heating elements; said horizontal support tube being connected in parallel with said first plurality of horizontal elements but in series with said second horizontal elements whereby steam passing through the support tube bypasses said first plurality of steam heating elements.

9. An apparatus as in claim 8 wherein at one location between each pass of the horizontal support tubes the support spacers are omitted. 

